1. Field of the Invention
The present invention relates to a method for correcting a thin-film formation program of a semiconductor device and a thickness measuring apparatus therefor, and more particularly, to a method for correcting a thin-film formation program of a semiconductor device and a thickness measuring apparatus therefor, which is capable of obtaining a desired thin film thickness while preventing process failures and delays.
2. Background of the Related Art
To maintain reliability in the characteristics of a semiconductor device, the thin-films formed on wafers in each manufacturing process must be of uniform thickness. Generally, the process of thin-film formation has many variables (e.g., temperature, time, pressure, and gas flow rate) according to the thin-film material. If the process variables deviate from a predetermined value for a thin-film formation program, the thickness of the thin-film to be formed departs from the standard. Accordingly, in order to keep the uniformity of thin-film thicknesses, accurate information must be secured regarding the thicknesses of thin-films in response to a change in the process variables. Also, whenever the thickness of the thin-film departs from the standard, the process variables of the program must be promptly changed.
FIG. 1 illustrates a process of correcting a thin-film formation program for a semiconductor device according to the prior art.
In Step 1, thin-films of a semiconductor device are formed in a thin-film deposition unit (e.g., sputtering equipment, chemical vapor deposition equipment or an oxidation/diffusion furnace). In Step 2, the thickness of the thin-film formed in Step 1 is measured by using a thickness-measuring apparatus with a mechanical stylus, for example, an M-gauge or ellipsometer. In Step 3, the measured thickness is compared with a standard thickness. If the thickness differential in Step 3 is greater than a predetermined allowable deviation, the exact process variables of the thin-film formation program are calculated in Step 4 for correcting the thin-film formation program.
On the other hand, if the thickness differential in Step 3 is less than the allowable deviation, it is assumed that the reliability in the characteristics of the semiconductor device can be maintained, and, as a result, the next process for forming a thin-film can proceed in Step 5 without the need for any correction of the process variables of the thin-film formation program.
However, if the decision in Step 3, regarding the difference between the measured thickness and the standard thickness, and in Step 4, regarding the correction for the thin-film forming program are both manually made, the following problems may occur: i) the thickness may depart from the standard due to a correction error; ii) delays occur when the thin-film formation equipment is idled while the uniformity of the thicknesses of thin-films is checked periodically; and iii) product damage may result should immediate correction not be made.
FIG. 2 is a cross section of a cooling chamber 100 where a wafer on which the metal deposition process has been completed is cooled, within metal deposition equipment according to the prior art.
In a metal deposition process, a wafer is usually heated to a high temperature. Referring to FIG. 2, a processed wafer 10 is cooled to room temperature on a pedestal 20. The cooling chamber 100 is isolated from the exterior by a chamber wall 50 and a chamber lid 60 installed atop the chamber wall. After the cooling process is completed, the processed wafer 10 is lifted by a wafer lifter 30. Then, an isolation valve 40 is opened to pass a robot arm (not shown) for wafer transfer. After the transfer of the processed wafer 10 is completed, the isolation valve 40 is closed again.
The cooling chamber having the above structure only performs the function of cooling a high-temperature processed wafer. After the wafer is transferred to the exterior, the thickness of thin-film on the wafer can be measured by various thickness-measuring apparatus in accordance with the type of thin-film. In general, the thickness measurements are manually performed by an operator. If the difference between the measured thickness and the standard thickness is larger than the allowable deviation, the process variables of the thin-film formation program are manually calculated and corrected.
As stated above, some problems may occur, such as, a departure from the thickness standard due to a mistake by an operator who is manually correcting the process variables of the program. Also, delays are caused when the thin-film forming equipment is idled while periodically checking the uniformity of the thin-film thickness. Finally, an increase in product damage may occur should immediate correction not be made upon departure from the standard thickness.